US20010007167A1 - Fabrication method of solid electrolytic capacitor - Google Patents

Fabrication method of solid electrolytic capacitor Download PDF

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Publication number
US20010007167A1
US20010007167A1 US09/750,795 US75079501A US2001007167A1 US 20010007167 A1 US20010007167 A1 US 20010007167A1 US 75079501 A US75079501 A US 75079501A US 2001007167 A1 US2001007167 A1 US 2001007167A1
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Prior art keywords
anodic oxidation
solid electrolytic
electrolytic capacitor
sintered body
fabrication method
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Abandoned
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US09/750,795
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English (en)
Inventor
Kazunori Watanabe
Hideaki Sato
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Tokin Corp
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NEC Corp
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Filing date
Publication date
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Assigned to NEC CORPORATION reassignment NEC CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SATO, HIDEAKI, WATANABE, KAZUNORI
Publication of US20010007167A1 publication Critical patent/US20010007167A1/en
Assigned to NEC TOKIN CORPORATION reassignment NEC TOKIN CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NEC CORPORATION
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
    • H01G9/0029—Processes of manufacture
    • H01G9/0032—Processes of manufacture formation of the dielectric layer

Definitions

  • the present invention relates to a fabrication method of a solid electrolytic capacitor and, particularly, to a surface processing method of an anode member in the form of a porous sintered body of a valve metal.
  • a fabrication method of a solid electrolytic capacitor having an anode of such a valve metal as tantalum is realized by forming a dielectric film on a surface of the anode in the form of a porous sintered body and forming a solid state electrolyte layer and a cathode layer on the dielectric film.
  • the dielectric film which is indispensable for a capacitor, is formed by anodic oxidation of the anode member formed of a valve metal, that is, forming an anode oxide film (Ta 2 O 5 ) having a predetermined thickness on the surface of the anode member by using anodic oxidation.
  • the present inventors have found that there is room for improvement on the leakage current characteristics of a solid electrolytic capacitor having an anode member formed according to the above mentioned conventional fabrication method and that the problem of the leakage current characteristics is due to natural oxidation (oxidation under condition in which chemical reaction energy is not supplied intentionally) of a sintered body in a custody during a time from a formation of the sintered body to a formation of the anode oxide film thereon by anodic oxidation.
  • the sintering step of, for example, tantalum at a temperature as high as 1200° C. to 1600° C. and lower than a melting point thereof. Therefore, the sintering is performed in a reduced pressure environment in the order of 1.33 ⁇ 10 ⁇ 4 Pa, in order to prevent the metal from being oxidized during the sintering.
  • the sintered body sintered in the sintering step is taken out from a sintering device after the temperature of the sintering device is lowered to, for example, 100° C. or less and gas within the sintering device is replaced by inert gas such as argon or nitrogen.
  • inert gas such as argon or nitrogen.
  • the sintered bodies Even if there is no need of transporting the sintered bodies to such far location, there may be a case where the sintered bodies must be in the custody for several days as goods in stock when a processing capacity of the anodic oxidation step is different from that of the sintering step.
  • the sintered bodies contact with oxygen in an atmospheric gas or air during the transportation or in the period of custody, so that natural oxidation proceeds.
  • the natural oxidation during transportation or custody degrades the leakage current characteristics of capacitors having sintered bodies, which are naturally oxidized. Further, depending upon the degree of oxidation, the sintered body may be decomposed by heat generated by oxidation and cannot be used in fabricating the anode member. When the sintered body is oxidized considerably, a custody canister thereof may be burned. Such spontaneous burning is so hard that it is impossible to use water to extinguish such spontaneous combustion since there is a risk of steam explosion. Therefore, it is necessary to other means for extinguishing fire by shutting out air with salt or sand.
  • the degree of influence of spontaneous combustion of sintered bodies during transportation or custody depends upon the number of sintered bodies in a canister, the density thereof in the canister, the amount of oxygen in the canister and/or the material of the canister, etc. However, it is a recent tendency that the frequency of spontaneous combustion and the adverse influence thereof are increased.
  • the possibility of spontaneous combustion thereof is higher than the conventional sintered body, since particle size of tantalum powder is finer and the surface area of the sintered body is larger enough to provide a larger contact area with air compared with the conventional technique.
  • the anode oxide film grown thereon in the anodic oxidation step is influenced by defects of the sintered body. Even in a case where the influence of defects does not lead the sintered body to spontaneous combustion, the leakage current characteristics of the solid electrolytic capacitor using the same anode oxide film is degraded compared with the conventional capacitor.
  • An object of the present invention is to provide a fabrication method of a solid electrolytic capacitor whose leakage current characteristics is improved by restricting excess growth of a natural oxide film in gas phase on a sintered body during a time from a completion of sintering to a start of an anodic oxidation step and preventing spontaneous combustion to thereby improve the safety of the sintered body in a custody.
  • the present invention is featured by performing a preliminary anodic oxidation as a preceding processing step for forming a dielectric film of a capacitor, in order to prevent the natural oxide film formed on the sintered body from becoming too thick.
  • the fabrication method of an anode member for a solid electrolytic capacitor in which a shaped member formed by shaping powder of a valve metal under pressure is sintered and the anode member is formed by forming an anodic oxidation film of the same metal as that of the sintered body on a surface of the sintered body, is featured by comprising, prior to the formation of the oxide film of the valve metal, the pre-anodic oxidation film forming step of preliminarily covering the surface of the sintered body with an oxide film of the same metal as that of the sintered body.
  • the fabrication method of the solid electrolytic capacitor comprises a shaped member forming step of shaping powder of a valve metal under pressure to form a shaped member having a predetermined shape, a sintering step of sintering the shaped member to form a sintered body, a step of forming a first anode member having a first anodic oxidation film formed on a surface of the sintered body by using an electrochemical processing device, an anodic oxidation step for forming a second anode member having a dielectric layer of the capacitor by forming a second anodic oxidation film on the first anode member after a predetermined time from a time at which the first anode member is derived from the electrochemical processing device, a step of forming a solid electrolytic layer on the dielectric layer of the second anode member and a step of forming a cathode layer on the solid electrolytic layer.
  • the first anodic oxidation film (pre-anodic oxidation film) is formed to have thickness larger than that of the natural oxide film existing on the surface of the sintered body.
  • the metal having valve function is tantalum
  • it is preferable that the first anodic oxidation film is made thicker than 1 nm and thinner than 10 nm.
  • anodic oxidation or barrel chemical conversion may be used as the pre-anodic oxidation film-forming step.
  • the barrel chemical conversion it is possible to form the pre-anodic oxidation film on surfaces of a plurality of sintered bodies by randomly putting the sintered bodies in an electrically conductive container formed with a plurality of holes and making the respective sintered bodies in contact with chemical conversion solution while rotating the container.
  • FIG. 1A to FIG. 1E show cross sections of an anode member in respective fabrication steps according to the fabrication method of the present invention
  • FIG. 2 illustrates an anodic oxidation method
  • FIG. 3 illustrates a barrel chemical synthesis method
  • a pre-anodic oxidation film 9 is formed by using a general anodic oxidation step.
  • a shaped member 1 in the form of a circular or polygonal pillar is formed by mixing tantalum powder and a binder, putting the mixture in a mold and pressing it.
  • a tantalum wire 2 is implanted in one end surface of the shaped member 1 .
  • the shaped member 1 is sintered at a temperature in a range from 1200° C. to 1600° C. under vacuum pressure of 1.33 ⁇ 10 ⁇ 4 Pa, resulting in a sintered body 3 .
  • This is the same as the conventional fabrication method.
  • the sintered body 3 is disposed in chemical conversion solution such as, for example, aqueous solution of phosphoric acid in opposing relation to an electrode 7 and a D.C. voltage, which is high, and a D.C. voltage, which is low, are applied to the tantalum wire 2 of the sintered body 3 and the electrode 7 , respectively.
  • Thickness of the tantalum pre-anodic oxidation film 9 to be formed must be larger than thickness of the tantalum oxide film formed by natural oxidation and smaller than thickness of the anodic oxidation film 4 as the dielectric member of the capacitor.
  • the chemical conversion voltage VA applied in the anodic oxidation step is determined by taking acceptable capacitance and leakage current characteristics of the resultant capacitor into consideration.
  • the voltage such that the anodic oxidation film 4 as the dielectric member of the capacitor becomes 10 nm to 250 nm thick. Therefore, it is preferable to form the pre-anodic oxidation film 9 of tantalum such that it is thicker than the natural oxide film and thinner than the anodic oxidation film formed in the subsequent anodic oxidation film-forming step. More preferably, the pre-anodic oxidation film 9 of tantalum is thicker than 5 nm and thinner than 10 nm.
  • the anodic oxidation film having predetermined thickness is formed by performing the original anodic oxidation step, which has been used to obtain the dielectric film thick enough for the capacitor.
  • the thickness of the anodic oxidation film is determined such that a total thickness of the anodic oxidation film and the pre-anodic oxidation film becomes equal to the thickness of the dielectric film, which is, for example, 10 nm or more, as shown in FIG. 1D.
  • a solid electrolytic layer 15 of, for example, manganese dioxide or electrically conductive high molecular material is formed on the dielectric layer 4 , that is, the anode member as shown in FIG. 1E and, further, a cathode layer 16 is formed by forming a graphite layer and a silver paste layer on the solid electrolytic layer in the order.
  • the tantalum wire 2 is welded to an external anode terminal and the cathode is adhered to an external cathode terminal by means of electrically conductive adhesive.
  • the assembly is molded by epoxy resin (not shown) and, after the external terminals are put in order, the tantalum solid electrolytic capacitor is completed.
  • the pre-anodic oxidation film 4 shown in FIG. 1C is formed by using barrel chemical conversion.
  • a plurality of sintered bodies 3 are randomly scattered in an electrically conductive container 11 , which is formed with a plurality of holes and rotatable about an electrically conductive rotation shaft 10 .
  • the pre-anodic oxidation films 9 are electrochemically formed on surfaces of the sintered bodies by making the respective sintered bodies in contact with chemical conversion solution 6 while rotating the container 11 .
  • a custody space for holding the sintered bodies for a time from the formation of the pre-anodic oxidation film until the next anodic oxidation step (FIG. 1D) is small compared with the first embodiment. Since, in the first embodiment, a plurality of sintered bodies are mounted on the metal belt with a constant interval and the pre-anodic oxidation is performed as mentioned previously, the sintered bodies with the pre-anodic oxidation films formed thereon are kept in custody as they are, so that the custody space becomes large due to space between adjacent sintered bodies. According to the second embodiment using barrel chemical conversion, however, it is possible to reduce the space between adjacent sintered bodies since the sintered bodies are separated independently. For the same reason as this, it is possible to improve the producibility in the pre-anodic oxidation film-forming step.
  • the barrel chemical conversion is used to form the pre-anodic oxidation film 9
  • the pre-anodic oxidation films 9 are scratched due to mutual contact of sintered bodies during the film formation.
  • the principle of the present invention resides on the reduction of contact area of the sintered body with air by forming the pre-anodic oxidation film 9
  • scratches on the pre-anodic oxidation film 9 is harmless in view of the effect to be obtained by the present invention.
  • the sintered body to be processed by barrel chemical conversion may or may not have an anode lead preliminarily implanted thereon.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
  • Powder Metallurgy (AREA)
US09/750,795 2000-01-12 2001-01-02 Fabrication method of solid electrolytic capacitor Abandoned US20010007167A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2000003428A JP2001196274A (ja) 2000-01-12 2000-01-12 固体電解コンデンサ用陽極体の製造方法
JP3428/2000 2000-01-12

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EP (1) EP1117110A3 (ja)
JP (1) JP2001196274A (ja)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090078344A1 (en) * 2007-09-24 2009-03-26 Gaffney Kevin M Tantalum anodes for high voltage capacitors employed by implantable medical devices and fabrication thereof
US9607770B2 (en) 2012-06-22 2017-03-28 Show A Denko K.K. Method for producing capacitor
CN109285703A (zh) * 2018-10-26 2019-01-29 中国振华(集团)新云电子元器件有限责任公司(国营第四三二六厂) 提高钽电容器耐压能力的方法及制作钽电容器的方法
US20230118528A1 (en) * 2021-10-20 2023-04-20 KYOCERA AVX Components Corporation Electrodeposited Dielectric for a Solid Electrolytic Capacitor

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8644003B2 (en) * 2005-06-09 2014-02-04 National University Corporation, Tokyo University Of Agriculture And Technology Electrolytic capacitor element and process for producing the same
CN103354178A (zh) * 2013-07-31 2013-10-16 株洲宏达电子有限公司 一种高压固体钽电容器介质氧化膜的制造方法
EP3139393A4 (en) * 2014-05-01 2018-02-21 Showa Denko K.K. Method for manufacturing tungsten-based capacitor element

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2700225A1 (de) * 1977-01-05 1978-07-13 Licentia Gmbh Verfahren zur anodischen oxidation von sinterkoerpern aus einem ventilmetall
NL7714173A (nl) * 1977-01-07 1978-07-11 Lignes Telegraph Telephon Werkwijze voor de anodische oxydatie van gefritte anoden.
US4131520A (en) * 1977-11-10 1978-12-26 Sprague Electric Company Two-stage anodization of capacitor electrodes
GB2140031B (en) * 1983-05-18 1985-11-20 Standard Telephones Cables Ltd Anodic oxidation of tantalum
JPH02277212A (ja) * 1989-04-18 1990-11-13 Matsushita Electric Ind Co Ltd タンタル電解コンデンサおよびその製造方法
JP3362600B2 (ja) * 1996-05-14 2003-01-07 松下電器産業株式会社 コンデンサの製造方法
JPH11150041A (ja) * 1997-11-19 1999-06-02 Hitachi Aic Inc 固体電解コンデンサの製造方法

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090078344A1 (en) * 2007-09-24 2009-03-26 Gaffney Kevin M Tantalum anodes for high voltage capacitors employed by implantable medical devices and fabrication thereof
US7837743B2 (en) * 2007-09-24 2010-11-23 Medtronic, Inc. Tantalum anodes for high voltage capacitors employed by implantable medical devices and fabrication thereof
US9607770B2 (en) 2012-06-22 2017-03-28 Show A Denko K.K. Method for producing capacitor
CN109285703A (zh) * 2018-10-26 2019-01-29 中国振华(集团)新云电子元器件有限责任公司(国营第四三二六厂) 提高钽电容器耐压能力的方法及制作钽电容器的方法
US20230118528A1 (en) * 2021-10-20 2023-04-20 KYOCERA AVX Components Corporation Electrodeposited Dielectric for a Solid Electrolytic Capacitor
US12002631B2 (en) * 2021-10-20 2024-06-04 KYOCERA AVX Components Corporation Electrodeposited dielectric for a solid electrolytic capacitor

Also Published As

Publication number Publication date
EP1117110A3 (en) 2006-04-19
EP1117110A2 (en) 2001-07-18
JP2001196274A (ja) 2001-07-19

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Owner name: NEC CORPORATION, JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WATANABE, KAZUNORI;SATO, HIDEAKI;REEL/FRAME:011417/0047

Effective date: 20001227

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Effective date: 20020606

STCB Information on status: application discontinuation

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